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TIOL111: Current limit is different between datasheet and custom board

Conor
Guru 10180 points
Part Number: TIOL111
Other Parts Discussed in Thread: TIOL112

Hi,

I am debugging a custom board with TIOL111 on it. TIOL111 can limit the current to the communication C/Q pin by inserting a resistor Rset between the 6th pin ILIM_ADJ pin and GND.

Looking at Figure 4 on page 8 and Table 1 on page 12 of the data sheet, the maximum value is 300 to 350 mA, and the upper limit can be further lowered by changing the Rset resistance value.

When I installed Rset of 10kΩ and checked, the current was 1.7 to 2.0A. From the calculation results in the datasheet, the upper limit should be 200-250mA.

The above confirmation is performed by connecting the C/Q pin and GND with 0.1Ω, and setting the C/Q pin to High by setting EN=High and TX=Low. The current value is calculated by checking the voltage across 0.1Ω using an oscilloscope. Current Fault Detection seems to be functioning, repeating the operation of stopping output at about 240us and restarting output at about 16ms.

Can you give me any comments?

Thanks,

Conor

  • 0
    TI__Mastermind 27030 points

    Hi Conor,

    It does sound like the TIOL111 is operating correctly and the current fault detection, indication, and auto recovery features are functioning.

    I'm sorry, but there is a slight misunderstanding about the term "current limit" and how the TIOL111 uses this term.  The TIOL111 uses this term "current limit" to designate the threshold for a current fault condition.

    The TIOL111 does not actively regulate, throttle, or prevent the current from exceeding a max value which is also commonly referred to as a "limit" and what I believe your current understanding of how the device should be operating.  Instead, the TIOL111 simply reports this over-current condition as a fault and disables the CQ output.

    There are some benefits to this behavior such as charging large capacitive loads that require large inrush currents for a short duration of time (less than tsc).

    But if you want an active limiting or regulation of the current, I would recommend the TIOL112 device instead of the TIOL111.  It is pin-to-pin compatible with the TIOL111 but it does contain current regulation so that the "current limit" set by the Rset resistor will actively restrict the current to this maximum level.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Guru 10180 points

    Hi Jonathan,

    I'm a little confused. Looking at the TIOL111 data sheet, it states that current can be limited by changing the resistor connected to the ILIM_ADJ pin.

       

    Is the following understanding correct?
    ・TIOL111 cannot limit CQ current. By adjusting RSET, it is possible to adjust Fault and recovery in current failure conditions.
    ・TIOL112 is capable of CQ Current Limit. By adjusting RSET, you can adjust the current limit and Fault and recovery for current fault conditions.

    Thanks,

    Conor

  • +1 in reply to Conor
    TI__Mastermind 27030 points

    Hi Conor,

    The term "limit" can be interpreted in two different ways and the way the TIOL111 datasheet uses the term is different than the one you are currently using.  The TIOl112 is however more in line with your current understanding of the term "limit.

    1. A point or level beyond which something does not or may not extend or pass
    2. A restriction on the size or amount of something permissible or possible.

    The TIOL111 uses the second definition of the term "limit."  The RSET resistor adjusts the maximum amount of current that is "permissible" before the device enters a Fault Condition and disables the CQ driver. 

    However, the TIOl111 does not "restrict" the current flowing through the CQ to a level that is equal to the "limit" set by the RSET resistor in the event the external load would want to consume more current such as during a short condition.  This would be consistent with the first definition of the term "limit."

    The TIOL112 differs from the TIOL111 in that it does contain the circuitry to "restrict" the current to the level set by the RSET resistor and therefore uses the first definition I have provided for the term "limit" and is consistent with your current interpretation of how the device should operate.

    The TIOL111 should not be used in applications that rely upon it to actively restrict the amount of current to a particular set level.  It will only monitor the current to make sure it does not exceed a set level or "limit" and if this limit is exceeded for longer than a time of tsc (200us typ), then it will enter a current fault condition and disable the CQ driver and assert the NFAULT pin.

    If you want a device that will act as a current limiter and restrict the amount of current to a set level or "limit," then you will want to use the TIOL112.

    Regards,

    Jonathan